Method for performing random access procedures and terminal thereof

ABSTRACT

A random access procedure between a mobile terminal and a network is performed based upon the characteristics of a RACH preamble. If the RACH preamble was explicitly signaled by the network, a downlink channel is monitored until a new transmission is indicated according to radio resource allocation information received from the network. If the RACH preamble was not explicitly signaled by the network, a contention resolution timer is started and the downlink channel is monitored until the contention resolution timer expires. Such monitoring of downlink channels in a more efficient manner, results in effective reduction in power consumption.

CROSS-REFERENCE

The present application claims priority benefit to the followingapplications, which contents are all incorporated by reference for allpurposes as if fully set forth herein: U.S. Provisional Application Nos.61/073,743 (filed Jun. 18, 2008), 61/074,998 (filed Jun. 23, 2008), andKorean Patent Application No. 10-2009-0048775 (filed Jun. 2, 2009).

BACKGROUND

The present invention relates to an apparatus and method for performingrandom access procedures. In the related art, random access procedureswere not performed efficiently. As such, the related art technologies donot sufficiently address such issues, and thus do not offer appropriatesolutions.

SUMMARY

The present inventors recognized at least the above-identified drawbacksof the related art. Based upon such recognition, the various featuresdescribed hereafter have been conceived such that a random accessprocedure between a mobile terminal and a network is performed basedupon the characteristics of a random access channel (RACH) preamble. Asa result, more efficient monitoring of downlink channels can beperformed, which results in reduced power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary network architecture for an E-UMTS (EvolvedUniversal Mobile Telecommunications System).

FIG. 2 shows an exemplary radio interface protocol architecture for thecontrol plane between the mobile terminal (UE) and the network (eNB,MME).

FIG. 3 shows an exemplary radio interface protocol architecture for theuser plane between the mobile terminal (UE) and the network (eNB, SAEGateway).

FIG. 4 shows an exemplary signal flow diagram of a contention basedrandom access procedure between the mobile terminal (UE) and the basestation (eNB).

FIG. 5 shows an exemplary relationship among certain channels (PDCCH andPDSCH) between the base station and mobile terminal.

FIG. 6 is a conceptual diagram to explain a contention based randomaccess procedure performed by the mobile terminal according to anexemplary embodiment.

FIG. 7 is a conceptual diagram to explain a non-contention based randomaccess procedure performed by the mobile terminal according to anexemplary embodiment.

FIG. 8 is a conceptual diagram to explain a contention based randomaccess procedure performed by the mobile terminal according to anexemplary embodiment for when the RACH procedure was unsuccessful.

FIG. 9 shows a flow chart of a random access procedure performed by themobile terminal according to an exemplary embodiment.

FIG. 10 is a conceptual diagram to explain the random access procedureof FIG. 9.

DETAILED DESCRIPTION

The inventive concepts and features herein are explained in terms of aLong Term evolution (LTE) system or other so-called 4G communicationsystems, which is an enhancement to current 3GPP technologies. However,such details are not meant to limit the various features describedherein, which are applicable to other types of mobile and/or wirelesscommunication systems and methods.

Hereafter, the term “mobile terminal” will be used to refer to varioustypes of user devices, such as mobile communication terminals, userequipment (UE), mobile equipment (ME), and other devices that supportvarious types of wireless communication technologies.

Embodiments of the present invention relate to sending and receivingdata between a base station (e.g. Node B, eNB, access point, etc.) and amobile station (e.g. mobile terminal, UE, user device, etc.) in a LongTerm Evolution (LTE) system. Power consumption of the mobile terminalcan be reduced to a minimum and a downlink channel can be moreeffectively monitored because a reception time for the downlink channelis determined according to the characteristics of a preamble for amobile terminal that performs random access.

Second generation (2G) mobile communications relate to transmitting andreceiving voice signals in a digital manner, and include technologiessuch as CDMA, GSM, and the like. As an enhancement from GSM, GPRS wasdeveloped to provide packet switched data services based upon GSM.

Third generation (3G) mobile communications relate to transmitting andreceiving not only voice signals, but also video and data. The 3GPP(Third Generation Partnership Project) developed the IMT-2000 mobilecommunication system and selected WCDMA as its radio access technology(RAT). The combination of IMT-2000 and WCDMA can be referred to as UMTS(Universal Mobile Telecommunications System), which comprises a UMTSTerrestrial Radio Access Network (UTRAN).

As data traffic is expected to increase dramatically, thestandardization for 3^(rd) generation mobile communications is underwayto establish a Long-Term Evolution (LTE) network that supports greaterbandwidth. LTE technologies are employed for an Evolved-UMTS (E-UMTS),which has an Evolved-UTRAN (E-UTRAN) that uses OFDMA (OrthogonalFrequency Division Multiple Access) as its radio access technology(RAT).

FIG. 1 shows the exemplary network architecture for an E-UMTS (EvolvedUniversal Mobile Telecommunications System) 100, which is a type ofmobile communications system. The E-UMTS system is a system that hasevolved from the UMTS system and its basic standardization tasks are nowbeing performed by the 3GPP organization. The E-UMTS system can be saidto be a Long Term Evolution (LTE) system, which is a type of so-called4G or next generation system that has evolved from the current 3G mobilecommunication systems.

The E-UMTS network 100 can be generally distinguished into the E-UTRAN(Evolved Universal Terrestrial Radio Access Network) 110 and the CN(core network). The E-UTRAN is comprised of a mobile terminal 112 (e.g.user equipment (UE), mobile station, handset, mobile phone, etc.), abase station 114, 116, 118 (e.g., an eNode B, access point (AP), networknode, etc.) a serving gateway (S-GW) 122, 124 located at an end of thenetwork for connection with an external network, and a mobilitymanagement entity (MME) 122, 124 that manages various mobility aspectsof the mobile terminal. For a single eNode B, one or more cells (orregions, areas, etc.) may exist.

FIGS. 2 and 3 show the radio interface protocol between the mobileterminal and base station based on the 3GPP radio access networkstandard. This radio interface protocol is divided horizontally into aphysical layer, a data link layer, and a network layer, and is dividedvertically into a user plane for transmitting data information and acontrol plane for transferring control signals (signaling). Theseprotocol layers can be divided into L1 (Layer 1), L2 (Layer 2), and L3(Layer 3), which are the lower three layers of the OSI (Open SystemInterconnection) standard model, which is well known in communicationsystems.

Hereafter, the control plane of the radio protocol in FIG. 2 and theuser plane of the radio protocol in FIG. 3 will be describedrespectively.

In Layer 1, the physical layer 225-245, 325-345 uses one or morephysical channels to provide an information transfer service. Thephysical layer is connected to the MAC (Medium Access Control) layer224-244, 324-344 located above via one or more transport channels, anddata is transferred between the MAC layer and the physical layer throughthese transport channels. Also, between respectively different physicallayers, such as the physical layer in the transmitter (transmittingside) and the physical layer in the receiver (receiving side), data istransferred via one or more physical channels.

The physical channels that exist for the physical layer in thetransmitting side and in the receiving side include: SCH(Synchronization Channel), PCCPCH (Primary Common Control PhysicalChannel), SCCPCH (Secondary Common Control Physical Channel), DPCH(Dedicated Physical Channel), PICH (Paging Indicator Channel), PRACH(Physical Random Access Channel), PDCCH (Physical Downlink ControlChannel) and PDSCH (Physical Downlink Shared Channel) and the like.

In L2 (Layer 2), the MAC layer provides service to a RLC (Radio LinkControl) layer 223-243, 323-343, which is an upper layer, via one ormore logical channels. Here, based upon the type of data beingtransmitted, the logical channels can be divided into control channelsthat are used to transmit control plane data, and traffic channels thatare used to transmit user plane data.

In L2 (Layer 2), the RLC layer supports the transmission of data withreliability. Each radio bearer (RB) is responsible to the guarantee ofQoS (Quality of Service) and transmits data accordingly. In order toguarantee the QoS that is unique to the RB, one or two independent RLCentities are provided for each RB, and three types of RLC modes (TM:Transparent Mode, UM: Unacknowledged Mode, and AM: Acknowledged Mode)are provided to support various QoS.

In L2 (Layer 2), the PDCP (Packet Data Convergence Protocol) layer322-342 in Layer 2 performs a header compression function to reduce theheader size for Internet Protocol (IP) packets that contain relativelylarge and unnecessary control information such that IP packets (such asfor IPv4, IPv6, etc.) may be effectively transmitted over the radiointerface having relatively small bandwidth. Also, the PDCP layer isused for performing coding of control plane (C-plane) data, such as RRCmessages. The PDCP layer can also perform coding of user plane (U-plane)data.

Located at the uppermost portion of Layer 3, the RRC (Radio ResourceControl) layer 222-242 is only defined in the control plane and isresponsible for the control of logical channels, transport channels andphysical channels with relation to the configuration, re-configurationand release of radio bearers (RBs). Here, a radio bearer is a serviceprovided by Layer 2 for transferring data between the mobile terminaland E-UTRAN. Here, the RB refers to a service provided by Layer 2 totransfer data between the UE and the E-UTRAN.

Hereafter, aspects of the RACH (Random Access CHannel) procedure will beexplained. The RACH procedure is used for transmitting relatively shortlength data via the uplink. In particular, the RACH procedure is usedwhen there is a signaling message or user data to be transmitted via theuplink by a mobile terminal that did not receive allocation of dedicatedradio resources, or may also be used when the base station shouldinstruct the mobile terminal to perform a RACH procedure.

Next, the random access procedure provided in an LTE system will beexplained. The random access procedure provided in the LTE system can beclassified as a contention based random access procedure and anon-contention based procedure. Such classification is based uponwhether the random access preamble is selected by the mobile terminalitself (i.e. preamble selected by the MAC in the mobile terminal) orselected by the base station (i.e. receiving information about thepreamble to be used through explicit signaling).

In a non-contention based random access procedure, the mobile terminaluses the preamble that was directly allocated to it from the basestation. Thus, if the base station had allocated a particular randomaccess preamble to the mobile terminal, such random access preamble isonly used by that mobile terminal, while other mobile terminals do notuse such random access preamble. Accordingly, because there is aone-to-one (1:1) relationship between the random access preamble and themobile terminal that uses such random access preamble, there are nocontentions (or conflicts) between multiple mobile terminals. In suchcase, upon receipt of such random access preamble, the base station canimmediately know which mobile terminal transmitted such random accesspreamble, and thus it can be said that more efficient operation ispossible.

In contrast, for a contention based random access procedure, because themobile terminal sends transmission upon selecting a particular randomaccess preamble among those that may be used, there is the possibilitythat multiple mobile terminals use the same random access preamble.Thus, even upon reception of a particular random access preamble, thebase station cannot accurately know which mobile terminal transmitted onsuch random access preamble.

The mobile terminal performs a random access procedure for at least thefollowing exemplary situations:

-   -   upon performing an initial access when there is no radio        resource control (RRC) connection with the base station;    -   upon initial access to a target cell while the mobile terminal        is in handover;    -   upon request by a command of the base station;    -   upon generation of data for the uplink, when uplink time        synchronization is not correct or when designated radio        resources to be used in appropriate requesting radio resources        have not yet been allocated;    -   during a correction (e.g. decoding, reconstruction, recovery,        etc.) procedure when there is a radio link failure or handover        failure.

Based upon the above explanations, the operations between the mobileterminal and the base station for a contention based random accessprocedure will be explained with reference to FIG. 4 (that includessteps 1 through 4).

Step 1)

In a contention based random access procedure, the mobile terminalselects (e.g. at random) one random access preamble among a set ofrandom access preambles indicated via system information or a handovercommand, then selects PRACH resources that can be used to transmit suchrandom access preamble, and then performs transmission. Here, suchpreamble is called a RACH MSG 1. When the mobile terminal itself(“randomly”) selects the preamble (i.e. the preamble selected by the MACitself, such is called a contention-based RACH procedure, and thepreamble is called a contention-based preamble. If the mobile terminalreceives allocation of the preamble directly from the network throughthe RRC or PDCCH (i.e. an explicitly signaled preamble), this is calleda non-contention based RACH procedure, and such preamble is called adedicated preamble.

Step 2)

After transmitting the random access preamble as selected above, themobile terminal attempts to receive its random access response within arandom access response reception window indicated from the base stationvia system information or handover command. In more detail, the randomaccess response information (typically called a RACH MSG 2) istransmitted in the form of a MAC PDU, which is delivered via the PDSCH,and the information related to the radio resources for the PDSCH isdelivered through the PDCCH via the RA-RNTI.

The random access response includes values comprising a random accesspreamble identifier (ID), a UL Grant (for uplink radio resources), aTemporary C-RNTI (a temporary cell identifier), and a Time AlignmentCommand (a value for time synchronization adjustment).

If the random access preamble identifier (ID) is the same as (i.e.matches) the random access preamble transmitted in step 1) above,especially while a contention based random access preamble procedure isin progress, the mobile terminal uses the information related to theuplink radio resources and performs the following step 3). If adedicated preamble is used in step 1), and if the random access preambleidentifier (ID) included in RACH MSG 2 and the random access preambletransmitted by the mobile terminal in step 1) are the same (i.e.matches), the RACH procedure is considered to be ended or terminated.

Step 3)

If the mobile terminal receives a random access response (RAR) that ismeant for itself (i.e. the RAR is a valid response for that mobileterminal), the information within such random access response isprocessed, respectively. Namely, the mobile terminal applies the TimeAlignment Command and stores the Temporary C-RNTI. Also, the UL Grant isused to transmit the data stored in its buffer or to transmit newlygenerated data to the base station. Here, the data transmitted by usingthe UL Grant (i.e., the MAC PDU) is commonly called RACH MSG 3. Amongthe data (i.e. RACH MSG 3) included in the UL Grant, the mobile terminalidentifier (ID) must be included. This is because in a contention basedrandom access procedure, the base station cannot determine which mobileterminal performed such random access procedure, and in order to preventor resolve any future contentions or conflicts, information that can beused to identify the mobile terminal would be required.

In the above procedure, there are two ways to include the identifier forthe mobile terminal. For the first way, if the mobile terminal alreadyhas a valid cell identifier (C-RNTI) allocated from the base station(eNB) of the corresponding cell before the random access procedure isperformed, the mobile terminal transmits such cell identifier via the ULGrant. For the second way, if the mobile terminal did not receiveallocation of a unique cell identifier from the eNB, the mobile terminalincludes its core network identifier (e.g., S-TMSI, Random ID, etc.) andperforms transmission. After transmitting data using the UL Grant, themobile terminal starts a contention resolution timer in order to solveany contention (conflict) problems.

Step 4)

After transmitting data (that includes its identifier) using the ULGrant included in the random access response, the mobile terminal waitsfor commands from the base station for resolving contentions. Namely,reception of the PDCCH is attempted in order to receive a particularmessage. There are two ways to receive the PDCCH. As stated previously,if the identifier transmitted by using the UL Grant is a cell identifier(C-RNTI) allocated to the mobile terminal from the eNB, the mobileterminal attempts reception of the PDCCH by using its cell identifier,and if the identifier is an identifier that was allocated through thecore network, attempt to receive the PDCCH is performed by using theTemporary C-RNTI included in the random access response.

Afterwards, for the former case (i.e. C-RNTI), if the PDCCH (referred toa RACH MSG 4 hereafter) is received (by using its cell identifier)before expiration of the contention resolution timer, then it isconsidered that the mobile terminal performed the ransom accessprocedure in a normal manner and the random access procedure is ended(terminated). For the latter case (i.e. Temporary C-RNTI), if the PDCCHwas received through the temporary cell identifier before expiration ofthe contention resolution timer, the data (referred to as RACH MSG 4hereafter), which is delivered by the PDSCH that is indicated by thePDCCH, is checked. If such data contains a unique identifier for themobile terminal itself, it is considered that the mobile terminalperformed the random access procedure in a normal manner, and the randomaccess procedure is ended (terminated). The message or MAC PDU receivedin this step 4) is commonly called RACH MSG 4.

Step 5)

In case the contention resolution timer has expired (i.e., a TemporaryC-RNTI or a cell identifier for the mobile terminal is not receivedbefore expiration of the contention resolution timer), the mobileterminal considers the RACH procedure to be a failure. As a result, anappropriate back-off timer is operated (started) and the RACH procedurebeginning from step 1) above is started again after expiration of suchback-off timer.

Hereafter, a method for the mobile terminal in an LTE system to receivedownlink data will be explained.

On the downlink, there are basically two types of physical channels:PDCCH and PDSCH. The PDCCH is not directly related to transmitting userdata, but used in transmitting control information needed forimplementing (or using) physical channels. In more basic terms, it canbe said that the PDCCH is used in controlling other physical channels.In particular, the PDCCH is used in transmitting information necessaryfor the mobile terminal to receive the PDSCH. With respect to data thatis transmitted at a particular point in time using a particularfrequency bandwidth, information about what mobile terminal such data isintended for, the size of such data being transmitted, and the like istransmitted via the PDCCH. Accordingly, each mobile terminal receivesthe PDCCH at a particular time (e.g., TTI: transmission time interval)and checks whether any data (that should be received) was transmitted.If there is an indication that data (which should be received) wasindeed transmitted, the PDSCH is additionally received by using theinformation (such as the appropriate frequency, etc.) indicated by thePDCCH. It can be said that information indicating as to what mobileterminal (i.e. a single UE or multiple UEs) the data of the PDSCH isbeing transmitted to, information indicating how the mobile terminal(s)should receive and decode the PDSCH data, and the like are transmittedvia a physical channel, i.e. the PDCCH (Physical Downlink ControlCHannel).

For example, in a particular sub-frame, let us assume that radioresource information A (e.g. frequency location), transmission formatinformation B (e.g. transmission block size, modulation and codinginformation, etc.), and RNTI (Radio Network Temporary Identity)information C undergo CRC (Cyclic Redundancy Check) masking andtransmitted via the PDCCH. One or more mobile terminals in acorresponding cell use the RNTI information that it has in order tomonitor the PDCCH, and referring to the above assumption, for a mobileterminal having RNTI information C, when the PDCCH is decoded, CRCerrors do not occur. Accordingly, such mobile terminal uses thetransmission format information B and radio resource information A todecode the PDSCH in order to receive data. In contrast, with respect tothe above assumption, in a mobile terminal that does not have RNTIinformation C, CRC errors occur when the PDCCH is decoded, and thus suchmobile terminal does not receive the PDSCH.

Through the above procedures, in order to inform about which mobileterminals have been allocated radio resources, a RNTI (Radio NetworkTemporary Identifier) is transmitted via each PDCCH, and such RNTI canbe classified as a dedicated RNTI or a common RNTI. A dedicated RNTI isallocated to a single mobile terminal and is used for transmitting andreceiving data corresponding to that mobile terminal. Such dedicatedRNTI is only allocated to those mobile terminals having theirinformation registered in the base station (eNB). In contrast, a commonRNTI is used by those mobile terminals that do not have theirinformation registered in the base station (eNB) and cannot be allocateda dedicated RNTI, in order to send and receive data with the basestation or used for transmitting information (such as systeminformation) that is commonly applied to a plurality of mobileterminals.

Meanwhile, the two main elements that comprise the E-UTRAN are the basestation and the mobile terminal. The radio resources for a single cellare comprised of uplink radio resources and downlink radio resources.The base station is responsible for the allocation and control of uplinkradio resources and downlink radio resources of a cell. Namely, the basestation determines what radio resources are to be used by what mobileterminals at certain moments in time. For example, the base station candetermine that 3.2 seconds from now, the frequency from 100 Mhz to 101Mhz will be allocated to user 1 for a duration of 0.2 seconds to allowdownlink data transmissions. Also, after the base station makes suchdetermination, these matters can be informed to the corresponding mobileterminal such that this mobile terminal receives downlink data.Likewise, the base station can determine when a certain mobile terminalshould use what amount of which radio resources for data transmissionvia the uplink, and the base station informs the mobile terminal aboutits determination, to thus allow the mobile terminal to transmit dataduring the determined time period using the determined radio resources.

Unlike the related art, if the base station manages radio resources in adynamic manner, efficient use of radio resources would be possible.Typically, a single mobile terminal continuously uses a single radioresource during a call connection. This is not preferable consideringthat most recent services are IP packet-based. The reason is that mostpacket services do not continuously generate packets during the durationof a call connection, and there are many time periods in which nothingis transmitted during the call. Despite this, continued allocation of aradio resource to a single mobile terminal is inefficient. To solvethis, the mobile terminal of a E-UTRAN system uses a method in whichradio resources are allocated to the mobile terminal only while servicedata exists.

Hereafter, some concepts of DRX will be explained. DRX refers todiscontinuous reception and signifies the operations about when (i.e. atwhen point in time) the base station should send information related toradio resource allocation to the mobile station during the process ofcommunication between the base station and the mobile terminal. Namely,a mobile terminal having to always monitor the downlink channel, inparticular the PDCCH, would result in undesirable power consumption forthe mobile terminal. Thus, to resolve this issue, the mobile terminaland the base station operate according to pre-established consistentrules, such that the base station sends radio resource allocationinformation via the PDCCH to the mobile terminal only at specific times.As a result, the mobile terminal only needs to monitor the PDCCH atcertain specified times, which reduces power consumption thereof.

Some types of DRX operations are performed in the following manner.

Initially, an active time is defined. This active time denotes the timeat which that the mobile terminal should wake up (from its idle state)to monitor a downlink channel, namely the PDCCH. After such active time,the mobile terminal need not monitor the PDCCH.

The active time may include the following types of time periods:

1) a time during which an On-Duration timer, or a DRX Inactivity timer,or a DRX Retransmission timer, or a Contention Resolution timer operates(=condition 1);

2) a time during which a Scheduling Request procedure is beingperformed;

3) a time during which a radio resource allocation message (forretransmissions) is sent, with respect to uplink transmissions;

4) a time during from after the RACH MSG 2 is transmitted up to the timewhen a C-RNTI or a Temporary C-RNTI (that indicates the allocation ofradio resources for an initial or new transmission) is received(=condition 4).

With reference to the technical description thus far, the technicalsolution provided by the embodiments of the present invention can bedescribed as follows.

In order to reduce power consumption, the DRX is performed also for theRACH procedure. The active time explained above can be considered inview of the RACH procedure.

FIGS. 6 and 7 shows RACH procedures performed by a mobile terminal for(a) Contention based and (b) Non-contention based situations. In (a)Contention based RACH, the active time denotes the time during which themobile terminal should monitor the downlink channel. In (b)Non-contention based RACH, unlike in contention based RACH, there is noRACH MSG 3 transmission being performed. Also, a Temporary C-RNTI is notused.

Referring to FIG. 6, when the mobile terminal monitors a downlinkchannel (namely, the PDCCH), in order to reduce power consumption,discontinuous receptions (DRX) are performed with respect to the RACHprocedure.

As this is a contention based random access procedure, the mobileterminal selects a preamble and this selected preamble is transmitted tothe base station (network) (see S1 and S2). If the mobile terminalreceives a random access response (RAR: RACH response, i.e. RACH MSG 2)from the base station, the information included in such random accessresponse are individually processed (S3). Also, as a procedure forreceiving a C-RNTI or a Temporary C-RNTI from the base station thatinforms about radio resource allocation, the mobile terminal sends data(i.e. a MAC PDU referred to as RACH MSG 3) via an uplink (UL) grant(S4). Additionally, the downlink channel (via which the C-RNTI or theTemporary C-RNTI will be transmitted) is monitored from the time whenthe preamble was selected until the C-RNTI or the Temporary C-RNTI isactually received (S5). Here, a DRX timer is operated (or started) andactive from after receiving the RACH MSG 2 until the C-RNTI or theTemporary C-RNTI is received. A contention based resolution timer isoperated (or started) after the RACH MSG 3 is transmitted until theC-RNTI or the Temporary C-RNTI is received.

FIG. 7 shows a conceptual diagram to explain a non-contention basedrandom access procedure performed by the mobile terminal according to anexemplary embodiment. When compared to FIG. 6, the mobile terminal doesnot perform the step of transmitting the RACH MSG 3 to the base station(i.e. S4 of FIG. 6 is not performed) in the non-contention basedsituation. Also, the Temporary C-RNTI is not employed in thenon-contention based situation. Here, the downlink channel monitoringperiod or duration of the RACH procedure is equivalent to that in FIG.6.

It should be noted that in FIG. 6, the Contention based RACH shows thesituation when the mobile terminal successfully performs the RACHprocedure. However, if the mobile terminal actually fails in performingthe RACH procedure, namely, if the C-RNTI or the Temporary C-RNTI is notreceived, then such failure situation in shown in FIG. 8.

In FIG. 8, active time 1 refers to the time duration as definedaccording to the active time condition 4 described above, while activetime 2 refers to the time duration as defined according to the activetime condition 1 described above.

As can been seen in FIG. 8, based upon the active time definitionsabove, the downlink channel must be monitored even during the back-offtime. However, the actual back-off time is not a time period duringwhich a contention resolution timer is being operated, and thus thenetwork does not allocate radio resources to the mobile terminal byusing the C-RNTI or the Temporary C-RNTI. Accordingly, because themobile terminal need not actually perform monitoring, power consumptionin unnecessarily wasted during this time period.

In order to solve this drawback, when performing a RACH procedure andmonitoring a downlink channel in order to receive schedulinginformation, the mobile terminal should receive the downlink channel isa more efficient manner.

To achieve this, it is proposed that the mobile terminal shoulddetermine whether or not downlink channel monitoring should be performedat a particular point in time (or during a specific time period) basedupon information regarding the type of on-going procedure that is beingperformed.

The mobile terminal may determine that it should monitor the downlinkchannel based upon whether or not the on-going procedure is a randomaccess (RACH) procedure.

In performing downlink channel monitoring, for the mobile terminal todetermine whether a particular time point (or period) is that for whichdownlink channel monitoring actually needs to be performed, and if theon-going procedure is a RACH procedure, then the information about thespecific type of RACH procedure being performed should be referred to.

Namely, the mobile terminal will determine whether downlink channelmonitoring should be performed or not by considering whether acontention based RACH procedure is being used or a non-contention basedRACH procedure is being used.

A contention based RACH procedure means that the mobile terminal selects(at random or by some other criteria) a RACH preamble to be used in theRACH procedure. Namely, in this case, it is assumed that the MAC entity(in the mobile terminal) begins the RACH procedure. Thus, such MACentity would select the preamble to be used.

A non-contention based RACH procedures means that the RACH procedure isperformed by the mobile terminal using a directly (explicitly) indicatedspecific RACH preamble.

The specifics for the above procedures will be further explainedhereafter.

Determining whether to receive the downlink channel according to thetype of RACH procedure is used refers to the following. After the mobileterminal begins the RACH procedure, it is checked whether the RACHprocedure is a contention based RACH procedure or a non-contention basedRACH procedure.

If a non-contention based RACH procedure, the downlink channel ismonitored during the period from when the RACH MSG 2 (i.e. random accessresponse) was received up until a C-RNTI (that indicates allocation ofradio resources for a new transmission) is received via the PDCCH.Namely, the time period, from after reception of the RACH MSG 2 (randomaccess response) until reception of the C-RNTI (that indicates radioresource allocation for a new transmission) via the PDCCH, is includedin the active time.

If a contention based RACH procedure, the downlink channel does not needto be monitored during the period from when the RACH MSG 2 (i.e. randomaccess response) was received up until a C-RNTI (that indicatesallocation of radio resources for a new transmission) is received viathe PDCCH. Namely, the time period, from after reception of the RACH MSG2 (random access response) until reception of the C-RNTI (that indicatesradio resource allocation for a new transmission) via the PDCCH, is notincluded in the active time.

In other words, with respect to the time period (or duration) thatbegins from when the RACH MSG 2 (i.e. random access response) wasreceived and ends when a C-RNTI (that indicates allocation of radioresources for a new transmission) is received via the PDCCH, such timeperiod is not included in the active time for contention based RACHprocedures, while such time period is included in the active time fornon-contention based RACH procedures.

Put differently, the active time definition according to condition 4(mentioned previously) is applied for instances where the RACH procedureis non-contention based (i.e., the RACH preamble is directly allocatedfrom an external source to the MAC entity), while such condition 4 isnot applied for other situations.

Thus, in embodiments of the present invention, the RACH procedure beingused is checked to see if it is contention based or non-contentionbased, and depending on such checking, the time period from reception ofthe RACH MSG 2 up to the reception of information via the PDCCH in theform of a C-RNTI that indicates radio resource allocation for a newtransmission, is included in the active time such that downlink channelreception can be determined.

FIG. 9 shows a flow chart of a random access procedure performed by themobile terminal according to an exemplary embodiment, while FIG. 10 is aconceptual diagram to explain the random access procedure of FIG. 9.

The MAC entity of the mobile terminal (UE) selects the RACH preamble,which is transmitted to the network (S10, S11). If the UE receives arandom access response (RAR: RACH MSG 2) from the network, theinformation included in such RAR is processed (S12). Namely, by usingthe information in the RAR, it is determined whether the RACH preamblewas selected by the MAC of the UE or explicitly signaled (or selected)by the network 9S13). If the RACH preamble was not selected by the MACof the UE, namely, if explicitly signaled by the network, the UEmonitors the downlink channel (PDCCH) until a new transmission isindicated by the radio resource allocation information (or schedulinginformation, such as C-RNTI) received from the network (S14).

However, if the RACH preamble was selected by the UE MAC, the contentionresolution timer is started (S15). As such, the operation in FIG. 9 canalso be understood from FIG. 10. Namely, as in the DRX procedure, whenthe UE receives a random access response (RAR: RACH MSG 2) from thenetwork, the contention resolution timer is operated and the downlinkchannel (PDCCH) is monitored. However, if a C-RNTI is not received uponexpiration of the contention resolution timer via the downlink channelbeing monitored, the UE performs the random access procedure again aftera back-off time is applied. Here, the downlink channel is not monitoredupon expiration of the contention resolution timer. The downlink channelis monitored when the random access procedure is performed again afterthe back-off time. As shown in FIGS. 9 and 10, as the UE does notmonitor the downlink channel during the back-off time, power consumptiondue to unnecessary DRX operations can be avoided.

The mobile terminal may include a communication module (which mayconsist of hardware, software, or a combination thereof that isconfigured to implement the operations described with respect to FIGS. 6through 10. Also, the mobile terminal according to the present inventionincludes various types of hardware, such as an input/output means (e.g.display screen, keypad, speakers, etc.) and a microprocessor (or othercontrol means) that provide control operations, as well as software usedto implement various operations.

FIG. 10 illustrates how the concepts in the embodiments of the inventivefeatures described herein can be implemented. Here, the situation wherethe mobile terminal failed in performing the RACH procedure, namely,when the C-RNTI or Temporary C-RNTI is not received, is shown.

As understood from FIG. 10, the active time defined according tocondition 4 (mentioned previously) is not applicable because acontention based RACH procedure is being used. Thus, during the time inwhich the back-off time is applied, the mobile terminal need not monitorthe downlink channel. As a result, undesired power consumption can bereduced.

Regarding the effects from implementing the embodiments describedherein, with respect to downlink channel monitoring performed by themobile terminal, the specific monitoring period (of the downlinkchannel, e.g. PDCCH) can be set in a more improved manner such thatbattery power efficiency (i.e. power source control) is enhanced.

Some more details about the concepts and features of the inventiveembodiments described herein can also be summarized as follows.

The DRX Command MAC CE may be used to put a UE directly into eithershort or long DRX Cycle. But when a DRX Command MAC CE is received whilethe DRX Short Cycle Timer is running, the timer should not be affected.If the timer is started again (i.e. re-started), the UE is further putin wake-up state, causing more battery consumption. This situation canoccur when HARQ Re-transmission Grant for a MAC PDU which includes theDRX Command MAC CE is received while the Short DRX Cycle Timer isrunning. Here, the terms “start” and “re-start” may be distinguishedsuch that “start” is used when the timer is not running, while“re-start” is used when the timer is running. Thus, when the Short DRXCycle Timer is running, it cannot be started, but it can be restarted.

However, such potential problem may be avoided by implementing thefollowing concept: when DRX Command MAC CE is received while Short DRXCycle Timer is running, the MAC CE is ignored.

The Active Time may include “a PDCCH indicating a new transmissionaddressed to the C-RNTI or Temporary C-RNTI of the UE has not beenreceived after successful reception of a Random Access Response (RAR).”This would cover the period between the time of RAR reception and thetime of starting the contention resolution timer. Otherwise, the UEwould monitor the DL channels longer than needed. For example, evenafter the contention resolution timer expires due to reception of notemporary C-RNTI, the UE would still monitor the DL channels.

However, such potential problem may be avoided by implementing thefollowing: setting the Active Time to include the period between thetime of successful reception of RAR and the time of starting theContention Resolution timer (for the case of contention-based preamble).

In other words, the situations for a contention-based preamble can beclarified as above. If UE has to wake up until the reception of C-RNTIregardless of other problems, the features described herein can beapplied to situations for a dedicated preamble.

The maintenance of Uplink Time Alignment will be explained.

The UE may have a configurable Time Alignment Timer. The Time AlignmentTimer is valid only in the cell for which it was configured and started.

If the Time Alignment Timer has been configured, the UE shall:

-   -   when a Timing Advance MAC control element is received:        -   apply the Timing Advance Command;        -   start the Time Alignment Timer (if not running) or restart            the Time Alignment Timer (if already running).    -   when a Time Alignment Command is received in a Random Access        Response message:        -   if the Random Access Preamble and PRACH resource were            explicitly signalled:            -   apply the Time Alignment Command;            -   start the Time Alignment Timer (if not running) or                restart the Time Alignment Timer (if already running).        -   else, if the Time Alignment Timer is not running or has            expired:            -   apply the Time Alignment Command;            -   start the Time Alignment Timer;            -   when the contention resolution is considered not                successful, stop the Time Alignment Timer.        -   else:            -   ignore the received Time Alignment Command.    -   when the Time Alignment Timer has expired or is not running:        -   prior to any uplink transmission, use the Random Access            procedure in order to obtain uplink Time Alignment.    -   when the Time Alignment Timer expires:        -   release all PUCCH resources;        -   release any assigned SRS resources.

Discontinuous Reception (DRX) will be explained. The UE may beconfigured by the RRC with a DRX functionality that allows it to notcontinuously monitor the PDCCH. The DRX functionality consists of a LongDRX cycle, a DRX Inactivity Timer, a DRX Retransmission Timer, andoptionally a Short DRX Cycle and a DRX Short Cycle Timer.

When a DRX cycle is configured, the Active Time includes the time:

-   -   while the On-Duration Timer or the DRX Inactivity Timer or a DRX        Retransmission Timer or the Contention Resolution Timer is        running; or    -   while a Scheduling Request is pending; or    -   while an uplink grant for a retransmission can occur; or    -   from the successful reception of a Random Access Response (RAR)        to the starting of the Contention Resolution Timer.

Here, the Active Time can also be defined as:

-   -   while a PDCCH indicating a new transmission addressed to the        C-RNTI of the UE has not been received after successful        reception of a Random Access Response, if the Random Access        Preamble was explicitly signaled; or    -   while the DL resuming timer is running. The DL resuming timer is        started when successful RAR is received in case that the Random        Access Preamble was explicitly signaled; (here, the DL resuming        timer is stopped when the C-RNTI of the UE is received)        (instead, it is also possible that the DL-resolution timer is        started when a dedicated preamble is received over the PDCCH)        or,    -   from the successful reception of a Random Access Response (RAR)        to the starting of the Contention Resolution Timer, if the        Random Access Preamble was selected by the UE MAC.

When a DRX cycle is configured, the UE shall perform the followingprocedures for each sub-frame:

-   -   start the On Duration Timer when [(SFN*10)+sub-frame number]        modulo (current DRX Cycle)=DRX Start Offset;    -   if a HARQ RTT Timer expires in this sub-frame and the data in        the soft buffer of the corresponding HARQ process was not        successfully decoded:        -   start the DRX Retransmission Timer for the corresponding            HARQ process.    -   if a DRX Command MAC control element is received:        -   stop the On Duration Timer;        -   stop the DRX Inactivity Timer.    -   if the DRX Inactivity Timer expires or a DRX Command MAC control        element is received in this sub-frame:        -   if the short DRX cycle is configured:            -   if the DRX Short Cycle Timer is not running, start the                DRX Short Cycle Timer;            -   use the Short DRX Cycle.        -   else:            -   use the Long DRX cycle.    -   if the DRX Short Cycle Timer expires in this sub-frame:        -   use the long DRX cycle.    -   during the Active Time, for a PDCCH-sub-frame except if the        sub-frame is required for uplink transmission for half-duplex        FDD UE operation:        -   monitor the PDCCH;        -   if the PDCCH indicates a DL transmission:            -   start the HARQ RTT Timer for the corresponding HARQ                process;            -   stop the DRX Retransmission Timer for the corresponding                HARQ process.        -   if the PDCCH indicates a new transmission (DL or UL):            -   start or restart the DRX Inactivity Timer.        -   if a DL assignment has been configured for this sub-frame            and no PDCCH indicating a DL transmission was successfully            decoded:            -   start the HARQ RTT Timer for the corresponding HARQ                process.    -   when not in active time, CQI and SRS shall not be reported.

Regardless of whether the UE is monitoring PDCCH or not the UE receivesand transmits HARQ feedback when such is expected.

The inventive embodiments described herein can further be described asfollows.

In the related art, the RACH preamble being contention based andnon-contention based was not distinguished when performing a RACHprocedure. This drawback can be overcome by defining the active time andcertain conditions thereof accordingly. The PDCCH needs to becontinuously monitored during the time between MSG2 and MSG 4. Afterreceiving the MSG 2, it is determined whether the RACH preamble iscontention based or non-contention based, and conditions are applied forsituations that are contention based or non-contention based.

Here, it should be noted that the features about contention based andnon-contention based RACH preambles could be described in other termsand expressions. For example, it can be said that a PDCCH indicating anew transmission addressed to the C-RNTI of the UE has not been receivedafter successful reception of a Random Access Response for theexplicitly signaled preamble. Here, the phrase ‘explicitly signaled’typically refers to dedicated signaling, but there may be somesituations where ‘explicitly signaled’ refers to non-dedicatedsignaling. Also, a preamble that is not explicitly signaled isequivalent to a preamble that is not selected by MAC. Additionally, ifthe PDCCH order is a specific value (=00000), then the procedure can goback to contention based.

This disclosure provides a method of performing discontinuous receptions(DRX), comprising: transmitting a RACH preamble to the network;receiving RAR (MSG 2) from the network; determining whether thetransmitted preamble was explicitly signaled by the network; ifexplicitly signaled, monitoring a downlink channel (PDCCH) until a newtransmission is indicated by a C-RNTI received from the network; and ifnot explicitly signaled, starting a contention resolution timer.

Also, this disclosure provides a method of performing discontinuousreceptions (DRX), comprising: transmitting a RACH preamble to thenetwork; receiving RAR (MSG 2) from the network; if the transmitted RACHpreamble was determined to be explicitly signaled by the network,monitoring a downlink channel (PDCCH) until a new transmission isindicated by a C-RNTI received from the network; or if the transmittedRACH preamble was determined to be not explicitly signaled by thenetwork, starting a contention resolution timer.

The features described herein can be summarized as follows.

A method of performing a random access procedure in a mobilecommunications system having a network and a mobile terminal, the methodperformed by the mobile terminal and comprising: transmitting a randomaccess channel (RACH) preamble to the network; receiving a RACH responsefrom the network that received the RACH preamble; monitoring a downlinkchannel using information included in the RACH response according towhether the RACH preamble is contention based or non-contention based;checking whether the random access preamble is contention based ornon-contention based; and performing a discontinuous reception procedureaccording to whether the random access preamble is contention based ornon-contention based.

Here, the information included in the RACH response can be used todetermine whether the random access preamble is contention based ornon-contention based. The monitoring can be performed until a newtransmission is indicated by a C-RNTI received from the network.

A method of performing discontinuous receptions (DRX) in mobilecommunications employing a network and a mobile terminal, the methodcomprising: transmitting a RACH preamble to the network; receivingrandom access response (MSG 2) from the network; monitoring a downlinkchannel (PDCCH) until a new transmission is indicated by a C-RNTIreceived from the network, wherein the monitoring is performed if thetransmitted RACH preamble was determined to be explicitly signaled bythe network; or starting a contention resolution timer, wherein thestarting is performed if the transmitted RACH preamble was determined tobe not explicitly signaled by the network.

The RACH preamble explicitly signaled by the network is a preamble thatis not selected by UE MAC. The RACH preamble explicitly signaled by thenetwork is information included in a PDCCH order.

A method of performing a discontinuous reception (DRX) procedure inmobile communications employing a network and a mobile terminal, themethod performed by the mobile terminal and comprising: starting arandom access procedure by sending a random access preamble to thenetwork; receiving a random access response from the network thatreceived the random access preamble; checking whether the random accesspreamble is contention based or non-contention based; and performing adiscontinuous reception procedure according to whether the random accesspreamble is contention based or non-contention based.

The discontinuous reception procedure is performed by either monitoringa downlink channel (PDCCH) if the random access preamble isnon-contention based or starting a contention resolution timer if therandom access preamble is contention based. The mobile terminal performsthe random access procedure if at least one of the following conditionsare met: upon performing an initial access when there is no radioresource control (RRC) connection with the base station; upon initialaccess to a target cell while the mobile terminal is in handover; uponrequest by a command of the base station; upon generation of data forthe uplink, when uplink time synchronization is not correct or whendesignated radio resources to be used in appropriate requesting radioresources have not yet been allocated; and during a correction, decodingor reconstruction procedure when there is a radio link failure orhandover failure.

Furthermore, the features described herein can be summarized as follows.

A method of performing a random access procedure between a mobileterminal and a network, the method comprising: transmitting a RACH(Random Access CHannel) preamble to the network; and monitoring adownlink channel by using information included in a RACH responsereceived from the network.

The monitoring step comprises determining whether the RACH preamble wasselected by a MAC entity of the mobile terminal by using the informationincluded in the RACH response. The downlink channel is furthermonitored_until a new transmission is indicated by a C-RNTI receivedfrom the network, if it is determined that the RACH preamble wasexplicitly signaled by the network. The method further comprising:starting a contention resolution timer, if it is determined that theRACH preamble was selected by the MAC entity of the mobile terminal. Thedownlink channel is a PDCCH (Physical Downlink Control CHannel).

A method of performing a random access procedure between a mobileterminal and a network, the method comprising: transmitting a RACH(Random Access CHannel) preamble to the network; receiving a RACHresponse from the network; monitoring a downlink channel until a newtransmission is indicated according to radio resource allocationinformation received from the network, if the RACH preamble wasexplicitly signaled by the network; and starting a contention resolutiontimer, if the RACH preamble was selected by a MAC entity of the mobileterminal.

If the contention resolution timer expires, the downlink channel is nolonger monitored. The downlink channel is a PDCCH (Physical DownlinkControl CHannel). The method further comprising: using the informationincluded in the RACH response to determine whether the RACH preamble waseither explicitly signaled by the network or selected by the MAC entityof the mobile terminal. The radio resource allocation information is aC-RNTI (Radio Network Temporary Identifier).

A method of performing a random access procedure between a mobileterminal and a network, the method comprising: transmitting a RACH(Random Access CHannel) preamble to the network; receiving a RACHresponse from the network; determining whether the RACH preamble wasexplicitly signaled by the network; if the RACH preamble was explicitlysignaled by the network, monitoring a downlink channel until a newtransmission is indicated according to radio resource allocationinformation received from the network; and if the RACH preamble was notexplicitly signaled by the network, starting a contention resolutiontimer.

The radio resource allocation information is a C-RNTI (Radio NetworkTemporary Identifier. The downlink channel is a PDCCH (Physical DownlinkControl CHannel). If the contention resolution timer expires, thedownlink channel is no longer monitored.

A mobile terminal comprising: a communications module configured totransmit a RACH (Random Access CHannel) preamble to the network, receivea RACH response from the network, determine whether the RACH preamblewas explicitly signaled by the network, monitor a downlink channel untila new transmission is indicated according to radio resource allocationinformation received from the network if the RACH preamble wasexplicitly signaled by the network, and start a contention resolutiontimer if the RACH preamble was selected by a MAC entity of the mobileterminal.

The various features and concepts described herein may be implemented insoftware, hardware, or a combination thereof. For example, a computerprogram (that is executed in a computer, a terminal or a network device)for a method and system for performing a random access procedure betweena mobile terminal and a network is performed based upon thecharacteristics of a RACH preamble may comprise one or more program codesections for performing various tasks. Similarly, a software tool (thatis executed in a computer, a terminal or a network device) for a methodand system for performing a random access procedure between a mobileterminal and a network is performed based upon the characteristics of aRACH preamble may comprise program code portions for performing varioustasks.

The method and system for processing random access procedures accordingto the present invention are compatible with various types oftechnologies and standards. Certain concepts described herein arerelated to various types of standards, such as GSM, WCDMA, 3GPP, LTE,IEEE, 4G and the like. However, it can be understood that the aboveexemplary standards are not intended to be limited, as other relatedstandards and technologies would also be applicable to the variousfeatures and concepts described herein.

INDUSTRIAL APPLICABILITY

The features and concepts herein are applicable to and can beimplemented in various types of user devices (e.g., mobile terminals,handsets, wireless communication devices, etc.) and/or network entitiesthat can be configured for performing a random access procedure in amobile communications system having a network and a mobile terminal.

As the various concepts and features described herein may be embodied inseveral forms without departing from the characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsscope as defined in the appended claims. Therefore, all changes andmodifications that fall within such scope or equivalents thereof aretherefore intended to be embraced by the appended claims.

1. A method of performing a random access procedure between acommunication terminal and a network, comprising: transmitting, by thecommunication terminal, a RACH (Random Access CHannel) preamble to thenetwork; receiving, by the communication terminal, a RACH response fromthe network; monitoring, by the communication terminal, a downlinkchannel according to a DRX (Discontinuous Reception) active time until aradio resource allocation for an initial transmission is indicatedaccording to radio resource allocation information received from thenetwork, if the RACH preamble was signaled by the network, wherein theDRX active time specifies a time until the radio resource allocation foran initial transmission is indicated if the RACH preamble was signaledby the network; and starting, by the communication terminal, acontention resolution timer and monitoring the downlink channel untilthe contention resolution timer is expired, if the RACH preamble wasselected by a MAC (Medium Access Control) entity of the communicationterminal, wherein the monitoring is not performed if the contentionresolution timer is expired.
 2. The method of claim 1, wherein thedownlink channel is a PDCCH (Physical Downlink Control CHannel).
 3. Themethod of claim 1, further comprising: using the information included inthe RACH response to determine whether the RACH preamble was eithersignaled by the network or selected by the MAC entity of thecommunication terminal.
 4. The method of claim 1, wherein the radioresource allocation information is a C-RNTI (Radio Network TemporaryIdentifier).
 5. A method of performing a random access procedure betweena communication terminal and a network, the method comprising:transmitting, by the communication terminal, a RACH (Random AccessCHannel) preamble to the network; receiving, by the communicationterminal, a RACH response from the network; determining, by thecommunication terminal, whether the RACH preamble was signaled by thenetwork; if the RACH preamble was signaled by the network, monitoring,by the communication terminal, a downlink channel according to a DRX(Discontinuous Reception) active time until a radio resource allocationfor a new transmission is indicated according to radio resourceallocation information received from the network, wherein the DRX activetime specifies a time until the radio resource allocation for an initialtransmission is indicated if the RACH preamble was signaled by thenetwork; and if the RACH preamble was not explicitly signaled by thenetwork, starting a contention resolution timer and monitoring thedownlink channel until the contention resolution timer is expired,wherein the monitoring is not performed if the contention resolutiontimer is expired.
 6. The method o claim 5, wherein the radio resourceallocation information is a C-RNTI (Radio Network Temporary Identifier).7. The method of claim 5, wherein the downlink channel is a PDCCH(Physical Downlink Control CHannel).
 8. A communication terminalcomprising: a microprocessor configured to provide control operations;an input/output means configured to operate based on the controloperations provided from the microprocessor; and a communications moduleconfigured to cooperate with the input/output means and operate based onthe control operations provided from the microprocessor, wherein thecommunications module is configured to transmit a RACH (Random AccessCHannel) preamble to a network, receive a RACH response from thenetwork, determine whether the RACH preamble was signaled by thenetwork, monitor a downlink channel according to a DRX (DiscontinuousReception) active time until a radio resource allocation for a newtransmission is indicated according to radio resource allocationinformation received from the network if the RACH preamble was signaledby the network, start a contention resolution timer if the RACH preamblewas selected by a MAC (Medium Access Control) entity of thecommunication terminal and monitor the downlink channel until thecontention resolution timer is expired if the RACH preamble was selectedby the MAC entity of the communication terminal, wherein the DRX activetime specifies a time until the radio resource allocation for an initialtransmission is indicated if the RACH preamble was signaled by thenetwork, wherein the communications module does not monitor the downlinkchannel if the contention resolution timer is expired.